Add //mojo/edk/platform/thread_utils.* containing "yield" and "sleep".

mojo/edk/util/cond_var_unittest.cc

Index: mojo/edk/util/cond_var_unittest.cc
diff --git a/mojo/edk/util/cond_var_unittest.cc b/mojo/edk/util/cond_var_unittest.cc
index ab966f1ba3a332eed6934ddab7c64e38f3b73a2a..4361a7386d1fd5f2d970c6942cb3b8507aa92e9b 100644
--- a/mojo/edk/util/cond_var_unittest.cc
+++ b/mojo/edk/util/cond_var_unittest.cc
@@ -11,16 +11,16 @@
 #include <type_traits>
 #include <vector>
 
-#include "mojo/edk/system/test/sleep.h"
+#include "mojo/edk/platform/thread_utils.h"
 #include "mojo/edk/system/test/stopwatch.h"
 #include "mojo/edk/system/test/timeouts.h"
 #include "mojo/edk/util/mutex.h"
 #include "mojo/public/cpp/system/macros.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
+using mojo::platform::ThreadSleep;
 using mojo::system::test::DeadlineFromMilliseconds;
 using mojo::system::test::EpsilonTimeout;
-using mojo::system::test::SleepMilliseconds;
 using mojo::system::test::Stopwatch;
 using mojo::system::test::TinyTimeout;
 
@@ -30,7 +30,7 @@ namespace {
 
 // Sleeps for a "very small" amount of time.
 void EpsilonRandomSleep() {
-  SleepMilliseconds(static_cast<unsigned>(rand()) % 20u);
+  ThreadSleep(DeadlineFromMilliseconds(static_cast<unsigned>(rand()) % 20u));
 }
 
 // We'll use |MojoDeadline| with |uint64_t| (for |CondVar::WaitWithTimeout()|'s